What does Node.js REPL stand for read eval print loop?

Understanding Node.js REPL: Read-Eval-Print-Loop

With the interactive command-line environment known as the Node.js REPL, developers may run JavaScript code directly and observe the results right away. It is an essential tool that comes with every Node.js installation and is helpful for debugging, discovering libraries, and rapidly testing code snippets.

The acronym for REPL is Read-Eval-Print-Loop. This name appropriately characterises its cycle of operation:

• Read: It reads the user’s JavaScript input.
• Eval: It evaluates the input code.
• Print: It prints the result of the evaluation to the console.
• Loop: It then loops back, waiting for the next input, until the user decides to exit.

Its constant feedback loop makes it a very useful tool for developers, particularly those who are new to JavaScript or Node.js, as it offers an instant environment for experimentation without requiring you to save and execute a file repeatedly.

Using the Node.js REPL

To start the REPL, simply open your terminal or command prompt and type node.

$ node
>

You’ll see a > prompt, indicating that the REPL is ready for your input.

Experimenting with JavaScript Expressions

Nearly any valid JavaScript expression or Node.js command can be entered straight into the REPL.

1. Basic Arithmetic
2. The REPL evaluates the expression right away and outputs the outcome.
3. String Functions:
4. Take note that the REPL may alter the quotation type for output strings, but the value remains unaffected.
5. Calling Functions: Node.js global functions such as console.log() can be called.
6. The console.log() function’s output to stdout is shown in the first line, Hi, while the function’s return value is left undefined.
7. Creating Variables: Once you create a variable in the REPL session, it remains available until you end it.
8. The variable assignment’s return value is shown by the undefined that appears after defining age. There are situations when console.log is not necessary because by default, any returned value will show on the screen.
9. Multi-line Blocks: JavaScript code with several lines is supported by the REPL. In order to signal that it needs additional input, it automatically changes the prompt to… when it notices an open bracket or an unfinished statement.

Mastering REPL Shortcuts and Commands

The REPL provides a number of “dot commands” and shortcuts to increase efficiency:

• Arrow Keys (Up/Down): The UP and DOWN arrow keys allow you to navigate through your command history. This is quite useful for executing or changing earlier commands again.
• .help: Provides an inventory of all REPL dot commands that are accessible.
• .break or .clear: By using the.break or.clear commands, you can return to the > prompt and end a multi-line expression without actually running it.
• .save filename: This saves all of the commands you’ve typed into the REPL window to a designated file.
• .load filename: This allows JavaScript code to be loaded and run in the current REPL session.
• Tab Key: Allows variables and predefined objects or methods to be autocompleted. If you type global. and hit Tab, for instance, all of the global objects you can access will be listed.
• _ (Underscore Variable): This unique variable holds the outcome of the previous action.

Exiting the REPL

You can exit the Node.js REPL in a few different ways to get back to the command prompt on your operating system:

• Press ENTER after typing .exit at the prompt.
• Hit CTRL+D.
• Twice press CTRL+C. The current command can be ended with the first CTRL+C, and the REPL can be exited with the second.

Your development process can be greatly streamlined and your knowledge of JavaScript and Node.js can be expanded by comprehending and making efficient use of the Node.js REPL.